function f() {
  console.log(new.target === f);
  console.log(this.property);
}

f(); // false
new f(); // true


var person = {
    name: '张三',
    describe: function () {
      return '姓名：'+ this.name;
    }
  };
  
  person.describe()
 
  // "姓名：张三"
  console.log( person.name);